The FBI has opened an investigation into a hacking attack against Twitter on Wednesday that affected some of the world’s highest-profile accounts, including those of former President Barack Obama and Tesla Inc. Chief Executive Officer Elon Musk.

“At this time, the accounts appear to have been compromised in order to perpetuate cryptocurrency fraud,” according to a statement from the FBI’s San Francisco office, which is leading the investigation. “We advise the public not to fall victim to this scam by sending cryptocurrency or money in relation to this incident.”

The announcement is significant because the FBI usually opens investigations in response to national security threats or attacks from foreign adversaries.

Hackers used hijacked accounts to obtain about US$120,000 in Bitcoin. Twitter said it was investigating the attack and taking steps to fix what went wrong.

The company moved to block posts from all verified accounts on the service for several hours as it sought to regain control over the hack. It later said that it had detected “a coordinated social engineering attack by people who successfully targeted some of our employees with access to internal systems and tools.”